Fillers and pigments are key components in many industrial markets, such as paper, paints, plastics, concrete, and pharmaceuticals. Fillers and pigments are utilized to reduce cost, improve functionality, and to improve the end use performance. One widely used pigment is titanium dioxide (TiO2), which is used to provide brightness and light scattering properties. Another widely used pigment is fumed silica, which may be added to some compositions to provide thixotropic attributes, for example, in paint products. A different product, but with a similar sounding name, is silica fume, which will also be further discussed below.
In paper products, commodity filler or pigment products such as synthetic precipitated calcium carbonate (PCC), or ground calcium carbonate (GCC) are often used. Various forms of PCC used include calcite crystalline structures, aragonite crystalline structures, and rhombohedral crystalline structures. Such crystalline structures are generally characterized by low aspect ratios, moderate brightness, and moderate light scattering power. Some of such materials provide improved optical properties. And, some of such materials enhance desired finished product attributes such as paper strength, when used in paper furnish, or print qualities, when used in paper coatings. However, there remains a significant need in various paper products for fillers and/or pigments which might improve light scattering power. Similarly, in certain paint products, and uses thereof, there remains a need for improved light scattering power in fillers and/or pigments.
Titanium dioxide is one of the most widely used pigments in many industries, such as paints, paper, coatings, and in some composites. Such use may often be to improve brightness, and/or to improve opacity. The property of improved opacity means that light scattering properties are improved, which provides a product that is harder to see-through. For example, thin papers may be made more opaque (i.e., made with see-through properties that make it look as if it were actually thicker) by the use of fillers with opacifying properties. The provision of such properties in products using titanium dioxide is primarily due to a combination of characteristics of titanium dioxide, such as a high refractive index (in the range of from about 2.49 to about 2.61), a small particle size (often in the 0.2 micron to 0.4 micron size), and in the manner in which adjacent particles of titanium dioxide pack together when used in various products. However, despite having a unique shape, size, and crystal structure, titanium dioxide has certain limitations. First, it has a very high density of about 4.2 grams per cubic centimeter. Further, in order to keep small titanium dioxide particles from agglomerating in various compositions, dispersants must often be used. Such dispersants usually have deleterious effects on strength properties, especially in the case of coated paper. Also, titanium dioxide particles are highly abrasive. Finally, due to the complexity of some widely used titanium dioxide manufacturing processes, which may include complex separation and purification processes, titanium dioxide is one of the most expensive fillers and/or coating pigments currently available.
Another filler and/or pigment that may be utilized in some applications is fumed silica. Fumed silica (also called pyrogenic silica) is generally manufactured from flame pyrolysis of silicon tetrachloride, or by the vaporization of quartz in a 3000° C. arc furnace. The primary particle surface area of most fumed silica is broadly in the range of from about 50 to about 600 square meters per gram. Furthermore, amorphous fumed silica particles may be fused into chainlike secondary particles which, in turn, agglomerate into tertiary 3-dimensional particles. One limitation of fumed silica material is that it is non-porous. Also, fumed silica is generally highly thixotropic, and consequently may cause high viscosity compositions, for example when added to paints and coatings. Also, the environmental impacts of the manufacturing processes for fumed silica, and the usually high cost of fumed silica, limit its use.
Silica fume (also called micro-silica, and not to be confused with the just discussed fumed silica) is an amorphous (i.e., non-crystalline) material. Silica fume is often collected as an ultra-fine powder as a by-product of silicon or ferro-silicon alloy production. Silica fume is generally in the form of spherical particles with an average particle size of about 150 nanometers. Silica fume has a surface area in the range of from about 15 to about 30 square meters per gram. Also, silica fume is a highly pozzolinic material, and thus may be used in cement and concrete to enhance compressive strength, bond strength, and abrasion resistance. However, at this time, silica fume, being a byproduct of production of other materials, is in relatively short supply.
With respect to the manufacture of amorphous silica compounds, U.S. Pat. No. 4,230,765, issued Oct. 28, 1980 to Takahashi et al., for NOVEL AMORPHOUS SILICA, and PRODUCTS THEREOF, describes methods for manufacture of various types of amorphous silica compounds from calcium silicate hydrates. However, he did not develop products of size and of certain characteristics to provide suitable performance for use in high performance paper coatings of that are described herein. Further, he did not recognize that by carefully controlling the reaction conditions, fixation of calcium carbonate phases to an amorphous silica substrate could be selectively determined, and in so doing, enhance properties provided by such products, especially for high performance paper coating compositions.
In summary, the just discussed fillers and/or pigments are generally of limited purpose. In many applications, each may have a single or limited number of product enhancing properties. Thus, there remains an as yet unmet need for a multi-functional filler and/or pigment that may, in many applications, replace expensive fillers and pigments such as titanium dioxide, fumed silica, or silica fume. It would be advantageous if such a new filler and/or pigment provided a combination of at least some ideal properties, such as (1) high surface ratio, (2) high aspect ratio, (3) high brightness, and (4) high light scattering coefficient. And, it would be even more advantageous if such a multi-functional filler and/or pigment were environmentally safe, and available at prices competitive with expensive fillers such as titanium dioxide, fumed silica, or silica fume. Consequently, it is believed that provision of a unique multi-functional filler and/or pigment would be an interesting and significant contribution to the art and science of fillers and pigments.
In the various figures of the drawing, like features may be illustrated with the same reference numerals, without further mention thereof. Further, the foregoing figures are merely exemplary, and may contain various elements that might be present or omitted from actual implementations of various embodiments depending upon the circumstances. An attempt has been made to provide the figures in a way that illustrates at least those elements that are significant for an understanding of the various embodiments and aspects of the developments described herein. However, various other elements for a multi-functional filler and/or pigment, especially as applied for various compositions using the same, may be utilized in order to provide useful, reliable, and highly functional fillers and/or pigments.